Maternal recognition of pregnancy

Maternal recognition of pregnancy is a crucial aspect of carrying a pregnancy to full term. Without maternal recognition to maintain pregnancy, the initial messengers which stop luteolysis and promote foetal implantation, growth and uterine development finish with nothing to replace them and the pregnancy is lost.

Pregnancy maintenance relies on the continued production of progesterone which is initially produced by the corpus luteum (CL). ^[1] A hormone secreting structure that develops on the ovary after ovulation. Maternal recognition of pregnancy differs between species, however they all include a signal to prevent luteolysis, which then prevents the resumption of menstrual or oestrous cycles.

Luteolysis is the regression of the corpus luteum. The process is identified by the decline of progesterone and it signifies the absence of pregnancy following ovulation. In the non pregnant uterus, the decline of progesterone allows the return of oestrogen, resulting in the upregulation of oxytocin receptors and consequently pulsatile release of  PGF2α. In turn, luteolysis is induced. This regression allows the continuation of the menstrual cycle.

However, if pregnancy is established, luteolysis is evaded via maternal recognition of pregnancy because high levels of progesterone are maintained by the CL and the placental hormone hCG further maintains the CL. ^[2]